Metal beverage cans are designed and manufactured to withstand high internal pressure—typically 90 or 100 psi. Can bodies are commonly formed from a metal blank that is first drawn into a cup. The bottom of the cup is formed into a dome and a standing ring, and the sides of the cup are ironed to a desired can wall thickness and height. After the can is filled, a can end is placed onto the open can end and affixed with a seaming process.
It has been the conventional practice to reduce the diameter at the top of the can to reduce the weight of the can end in a process referred to as necking. Cans may be necked in a “spin necking” process in which cans are rotated with rollers that reduce the diameter of the neck. Most cans are necked in a “die necking” process in which cans are longitudinally pushed into dies to gently reduce the neck diameter over several stages. For example, reducing the diameter of a can neck from a conventional body diameter of 2 11/16th inches to 2 6/16th inches (that is, from a 211 to a 206 size) often requires multiple stages, often 14.
Each of the necking stages typically includes a main turret shaft that carries a starwheel for holding the can bodies, a die assembly that includes the tooling for reducing the diameter of the open end of the can, and a pusher ram to push the can into the die tooling. Each necking stage also typically includes a transfer starwheel shaft that carries a starwheel to transfer cans between turret starwheels.
The starwheel shafts and the main turret shafts each include a gear, wherein the gears of each shaft are in meshed communication to form a continuous gear train. In conventional can necking systems, a single motor is used to provide the torque required to drive the entire gear train at high speeds. In some circumstances, such as when personnel safety is implicated, an emergency requires rapid stopping of the turrets. An emergency stop put a high torque load on the gear teeth compared with normal operation. Start up conditions may also create relatively high torque load on some gear teeth.
There is a general need for improved driving configurations for necking machines.